The company notes this marks an increase of 50 million songs since March when it announced 300 million sales.

The Register notes that the figures "show that Apple's digital music strategy has more legs than iPod hardware sales," but it questions how many iTunes Music Store customers regularly purchase music – the iTunes Music Store equivalent of the Napster subscriber.

"That figure is likely to be well below the iPod owner tally, but probably higher than Napster's subscriber base of 410,000 or MusicNet's total number of subscribers, 500,000," the report suggests.